The present invention relates to a digital telephone which can be provided with services of voice (referring to voice data) and data (referring to non-voice data) at the same time and, in particular, to a circuit which separates received data formed of a basic access frame into voice, data and signaling information.
Generally, the digital telephone is provided with the services of voice and data according to a time compression multiplexing (hereinafter referred to as TCM) transmission method, by being connected to a private branch exchange (PBX) or a key telephone system equipped with a digital network.
The frame structure of basic access is one of the frame structures of integrated service digital network (hereinafter referred to as ISDN) which arose in response to an increase in communication caused by the congestion of information and knowledge. It is formed of two B channels which can provide voice and data at the same time and of one D channel which transmits information for control. In other words, it is of 2B+D channeled structure. The transmission format according to said TCM transmission method becomes like A and B in FIG. 1. The A in FIG. 1 is the transmission format on the private branch exchange or key telephone system and the B in FIG. 1 is the transmission format in the digital telephone. The data format of basic access becomes like C in FIG. 1. The C in FIG. 1 corresponds to the transmission frame Tx or reception frame Rx in A and B of FIG. 1, respectively. The synchronization information SY1, SY2, signaling information SG1, SG2 and null bits in C of FIG. 1 correspond to D channel, while voice and data correspond to B1 channel and B2 channel, respectively.